Type 1 diabetes (T1D) occurs in genetically predisposed individuals as a result of the progressive, selective destruction of pancreatic ?-cells, which is primarily mediated by autoreactive T cells. The disease process results in loss of insulin secretion and life-long insulin-dependence, and unfortunately, most often occurs in children, adolescents, and young adults. Years later, these individuals are at risk of developing chronic complications, which can be severely debilitating and life-threatening. The process of ?-cell destruction begins long before clinical disease onset and continues after development of hyperglycemia; at the time of diagnosis subjects retain a significant amount of ?-cell function as measured by C-peptide responses to a mixed meal tolerance test (MMTT). However, ?-cell function continues to deteriorate after diagnosis with the presumed eventuality of near complete loss of secretion over time. At present there is no treatment that fully interdicts islet autoimmunity. However, clinical trials have shown promising results, demonstrating that it is possible to interfere with islet autoimmunity and preserve C-peptide secretion for at least some time. Diabetes TrialNet is a consortium of international researchers, NIH-funded, investigating interventions for the prevention or delay of type 1 diabetes. As a TrialNet Clinical Center our long-term scientific goals are to contribute to the overarching goals of TrialNet: develop a better understanding of the natural history and molecular basis of T1D and implement clinical trials evaluating new strategies to prevent this disease. The objective of this proposal, a step in pursuit of these goals, is to remain an active participant in the research network, Type 1 diabetes TrialNet, and in the process of designing and implementing new prevention strategies. Each investigative step taken toward modulating the destructive process that leads to T1D moves us closer to the ultimate goal of prevention.